1. Field of the Invention
The field of the present invention is a digital bus for facilitating transfer of data between digital data collection devices. The field of the invention is also a multiple computer system and associated digital bus by which data can be rapidly transmitted between the various computers.
2. Description of the Prior Art
Heretofore, various systems have been proposed for facilitating the transmission of digital data from one digital device, such as a computer, in a group of such digital devices to any other device in the group. In computer terminology, this can be stated as a transmission of data from any node in a network to any other node. In such systems it is highly desirable to have rapid transfer of data between the various computers. Also it is desirable in such systems to have high reliability and low complexity of components (hardware) and low cost of components. In an attempt to meet this criteria, several systems have been proposed.
In one system including a plurality of, for example five, computers, direct connection is made between each pair of computers. High throughput of data between the computers is an advantage of this system since data can be transmitted between many pairs of computers simultaneously. Reliability is also high for this system since failure of a single computer does not affect the data path between the other computers. However, the hardware, circuitry, components and transfer lines, are clearly quite complex and costly.
Another system utilizes a central computer to which other computers are connected and through this central computer all data passes. The complexity of the hardware, circuitry and circuit components are at a low, acceptable level in this system. However, the throughput capacity for transfer of data is reduced since only one data transfer can take place at a time. More importantly, reliability is low since failure of the central computer is equivalent to failure of the entire multiple computer system.
In still another system, a circular arrangement of computers is established with line connections between adjacent computer devices in the circle. In this system, data received by one computer that is to be received by another computer in the circle is transferred from computer to computer until it reaches the receiving computer for which it was destined. The complexity of the circuitry and components thereof (hardware) is not too great and is at an acceptable level. However, failure of a single computer can result in total system failure. To avoid total system failure, elaborate schemes have been proposed for rerouting the data in an opposite direction if a computer is not operational. Again, however, failure of more than one computer will result in failure of the system. Also in the normal operation of this circular system an undesirable delay is introduced at each stop at a computer on the circular path during the transmission of data between non-adjacent computers.
As will be described in greater detail hereinafter, the digital bus of the present invention and a multiple computer system incorporating same avoid and/or minimize many of the shortcomings described above by providing a linear digital data bus. As will be explained in greater detail below, the complexity of the circuit components (hardware) is at an acceptable level since only one digital bus is required along with as many computer/interface/controller/coupling units or subsystems (hereinafter computer/controllers) as are required for the particular multiple computer system. Any computer/controller can be removed from the digital bus deliberately or through failure without affecting the other computer/controllers. Reliability of the system is therefore high. Also rapid transmission of data is achieved with the digital bus of the present invention. However, simultaneous transfer of data between more than two computers cannot be achieved with this system.